Concrete masonry units are typically produced using a production machine and a mold assembly. Generally, the mold assembly includes a mold having mold cavities and a tamperhead. The production machinery may drive the tamperhead into the mold to strip formed and compacted concrete products from the mold cavities.
The tamperhead may be composed of several sub-components which may include an upper head structure, a plunger and a stripper shoe. Multiple sets of stripper shoes and plungers may be connected to a single head structure and may be used to strip multiple masonry units from one or more molds or a set of concrete mold cavities. The plungers are commonly fabricated in structural shapes, depending on the shape and type of concrete units being formed. Plungers typically include a rigid material such as steel and are welded on one end to the head structure and on the other end to the stripper shoe. The plungers provide the structural load path to compress the concrete and strip the formed concrete product from the mold.
Upon filling the mold with concrete, the tamperhead may be lowered until the stripper shoes enter the mold cavities and contact the concrete. However, the stripper shoes and the mold cavities must be particularly aligned. In previous systems, this alignment process may inflict significant wear and stress on both the mold and tamperhead, resulting in increased production time and cost.
By design, a stripper shoe mounted on a tamperhead needs to fit a respective mold cavity with a minimal clearance. Depending on the type and size of product being manufactured, this clearance may range from 0.20 mm to 1.50 mm per side. If the clearance is too small, the shoe will abrade against the cavity wall, thereby inducing stress in the mold and production machinery as well as premature wear on the machinery. If the clearance is too large, concrete will extrude between the shoe and the cavity walls, forming “burrs” on top of the product which, at best, detract from its aesthetic appeal and, at worst, create installation problems in the field.
Typically, the production machinery is incapable of guiding the tamperhead and the mold within the exacting minimal clearance required. As a result, prior machines have included a leading angle on the top edge of the mold cavities. This leading angle may serve as a default guidance and alignment mechanism. The alignment of the stripper shoes with the mold cavities occurs, contemporaneously with the lowering of the tamperhead, when the leading angle on the mold cavities forces and guides the stripper shoes into the openings of the mold.
The demands and economics of the concrete product production industry result in the need to run the production machinery at high speeds and high volumes. As a consequence, a stripper shoe may impact the leading edge of a mold cavity repeatedly and at high impact forces. The impact of the stripper shoe on the leading edge varies from one machine to another because different production machines use different systems to drive a compression beam. For example, some production machines use a hydraulic system while others use a mechanical system at varying speeds and vibration frequencies. Moreover, the operator of the machines may vary the speed of the compression beam as the produced concrete products may require. Nevertheless, this impact causes significant forces and vibrations in the mold cavities and in the tamperhead. These impact forces and vibrations are considered a significant factor in the failure of tamperheads and, more particularly, in the failure of plungers. Furthermore, severe impacts between the stripper shoes and the mold may cause significant damage to the mold and, in some cases, may result in catastrophic failure of the mold by crushing the thin walls separating the individual mold cavities.
While the tamperhead and the mold cavities may be initially aligned during insertion of the tamperhead and the mold into the production machinery, this alignment is not sufficient once the machinery is used for production of concrete products. The forming process includes vibrating or shaking of the mold assembly with a vibration system as the concrete is compacted. This vibration system spreads the concrete material evenly within the mold assembly cavities to produce a more homogeneous concrete product and assist in compacting the concrete product. Unfortunately, vibrations of the mold assembly transfer forces and stresses to the tamperhead and mold cavities, thereby causing small variations in the position of the production machinery. These vibrations typically occur approximately every eight to fifteen seconds during a typical production cycle depending on the type of concrete product being formed.
Unfortunately, the repeated forces transmitted by the alignment impact forces and vibrations makes the plunger and joints in the tamperhead susceptible to material fatigue failure and cause wear and stress on the mold. As a result of the combined stresses and wear, expensive plungers typically last for only a short period of time and must be replaced at great expense and loss of production time. Likewise, damaged mold cavities must be replaced or repaired, requiring significant and costly machining.
Therefore, there exists a need for a tamperhead and mold that repeatedly aligns itself during each production cycle, thereby reducing the resultant fatigue stresses and wear from repeated alignment impacts.